Disclosed is a system for detecting an attack, which includes a server and a plurality of vehicles capable of wirelessly communicating with each other. Each of the vehicles has a sensor, a sensor information acquisition unit, a traffic information reception unit, and a transmission unit that transmits the sensor information and the traffic information to the server. The server has a reception unit that receives the sensor information and the traffic information from the vehicles, a verification unit that verifies whether the sensor information and the traffic information are inconsistent with each other, and a notification unit that notifies, when the sensor information and the traffic information are inconsistent with each other, the vehicles of the inconsistency.